In conventional rolling bearings, their operating state has been checked with one or two temperature sensors, a rotational speed sensor and a sensor for sensing an abnormal vibration. These sensors are attached to a member disposed near the rolling bearing or to a fixed ring composed of the bearing. Also, detection of a load applied to the rolling bearing during operation has conventionally been inadequate. For example, a rolling bearing disclosed in U.S. Pat. No. 4,145,930 issued Mar. 27, 1979, is provided with two pairs of strain gauges (1, 2; 3, 4) arranged on and along one of the opposite side surfaces of a fixed ring (9) for sensing the rotating speed of a rolling ring (5) in the bearing (8). However, this prior bearing is not provided with any one of the above-mentioned sensors or detectors other than the rotating speed sensor.
Accordingly, in operation of such prior bearings, the bearings are prone to overheating or seizing-up because they have no means for sensing beforehand an abnormal increase in the load applied to them. Also, it is difficult to know in advance that the bearing has been considerably flaked due to its rolling contact fatigue and is thus approaching the end of its fatigue life. In addition, if the bearing is provided with a conventional set of load indicator, rotational speedometer, vibrometer, thermometer and the like for checking performance characteristics of the bearing, such a set of detectors requires a relatively large space for its arrangement and is also high in cost.